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Image Loader Registration

This example shows how to register custom image loader so that library functions such as gp_load_image() and gp_save_image() can use it.

// SPDX-License-Identifier: GPL-2.1-or-later
/*
 * Copyright (C) 2009-2014 Cyril Hrubis <metan@ucw.cz>
 */

 /*

   Shows how to register custom image loader/saver.

   Feed it with small image (cca 60x60 pixels) to produce ASCII art version.

  */

#include <stdio.h>
#include <string.h>
#include <errno.h>

#include <gfxprim.h>

/*
 * Saves 2 bpp grayscale image as ASCII Art
 */
static int write_data(const gp_pixmap *img, gp_io *io,
                      gp_progress_cb *callback)
{
        gp_io *bio;
        int err;

        if (img->pixel_type != GP_PIXEL_G4) {
                errno = ENOSYS;
                return 1;
        }

        /* Create buffered I/O */
        bio = gp_io_wbuffer(io, 0);

        if (!bio)
                return 1;

        unsigned int i, j;
        const char *const table[] = {" ", ".", ",", "-", "=", "#", "O", "$"};

        for (j = 0; j < img->h; j++) {
                for (i = 0; i < img->w; i++) {
                        gp_pixel p = gp_getpixel_raw(img, i, j);
                        const char *c = table[p>>1];

                        err = gp_io_flush(bio, c, 1);
                        if (err)
                                return 1;
                }

                if (gp_io_flush(bio, "\n", 1))
                        return 1;

                if (gp_progress_cb_report(callback, j, img->h, img->w)) {
                        errno = ECANCELED;
                        return 1;
                }
        }

        gp_io_close(bio);
        gp_progress_cb_done(callback);
        return 0;
}

static gp_pixel_type save_ptypes[] = {
        GP_PIXEL_G4,
        GP_PIXEL_UNKNOWN,
};

const gp_loader loader = {
        .Write = write_data,
        .save_ptypes = save_ptypes,
        .fmt_name = "ASCII Art",
        .extensions = {"txt", NULL},
};

int main(int argc, char *argv[])
{
        gp_pixmap *c, *gc, *sc;

        gp_loader_register(&loader);

        /* List all loaders */
        gp_loaders_lists();
        printf("\n\n");

        if (argc != 2) {
                fprintf(stderr, "ERROR: Takes image as an argument\n");
                return 1;
        }

        /* Now load image and save it using our loader */
        c = gp_load_image(argv[1], NULL);
        if (c == NULL) {
                fprintf(stderr, "Failed to load image: %s\n", strerror(errno));
                return 1;
        }

        /*
         * Font letters are not square resize the image so that it's twice it
         * original width.
         */
        gp_size w = 120;
        gp_size h = (w/2 * c->h + c->w/2)/c->w;

        sc = gp_filter_resize_alloc(c, w, h, GP_INTERP_LINEAR_LF_INT, NULL);
        gc = gp_filter_floyd_steinberg_alloc(sc, GP_PIXEL_G4, NULL);

        if (gc == NULL) {
                fprintf(stderr, "FloydSteinberg: %s\n", strerror(errno));
                return 1;
        }

        printf("Saving to test.txt\n");

        if (gp_save_image(gc, "test.txt", NULL)) {
                fprintf(stderr, "Failed to save image: %s\n", strerror(errno));
                return 1;
        }

        return 0;
}